In the past, an Ethernet, the same applies in the following explanation) is known as a system for performing transmission and reception of data between communication nodes connected by a cable. As a connection form of communication nodes in the Ethernet, bus topology, star topology, line topology, and the like are known (see, for example, Non-Patent Literature 1).
The bus topology is configured by, with one cable serving as a trunk line set as the center, extending branch cables from the center at appropriate intervals and arranging a plurality of communication nodes. In this bus topology, when the communication nodes simultaneously transmit data, collision of the data occurs. Therefore, a CSMA/CD (Carrier Sense Multiple Access/Collision Detection) system for, while avoiding collision, securing a transmission right and propagating the data to all connected communication nodes is adopted to perform transmission of the data.
However, as a connection form of communication nodes in recent years, the star topology is mainly used. This star topology has a configuration in which, with a communication node called switching hub having a plurality of ports set as the center, other communication nodes are connected to the ports of the switching hub via a cable such as a UTP cable (Unshielded Twisted Pair Cable). The switching hub also has a buffer memory. Even when a plurality of communication nodes simultaneously transmit data, after accumulating the data in the buffer memory, the switching hub transmits the data to all ports other than a port at a transfer destination or an arrival port. Therefore, unlike the bus topology, it is unnecessary to take into account collision of the data.    Non-Patent Literature: “Impress Standard Textbook Series Revised Edition 10 Gigabit Ethernet Textbook”, compiled under the supervision of Osamu Ishida and Koichiro Seto, Kabushiki Kaisha Impress Network Business Company, Apr. 11, 2005